An injection molding machine operates so rapidly that it can quickly finish a run of a particular molded part in a comparatively short period of time. In view of the substantial cost of the machine, it cannot be allowed to sit idle. The mold base in the machine has to be removed and a new mold base inserted so that the machine can continue to operate. The time taken in changing the mold base must be limited so the machine can again begin productive use. It currently takes from one to several hours to complete a mold base change. This lost time has a marked effect on the profitability of a company.
In order to speed up the mold change process, attempts have been made to equip the platens of the molding machines with an array of clamps and guides for supporting the mold base. For example, U.S. Pat. No. 4,500,274 issued to Cyriax et al. discloses a quick change mold assembly employing a plurality of spaced hydraulic clamps mounted on each platen of the press. Spaced guides are provided for receiving a plate attached to the back of a mold half. The clamps and guides are fastened directly to the platens. In order to add these parts, the press has to be disassembled so that the face of the platen can be drilled and tapped. There is no convenient way for machining the platen in the machine. After the platen is prepared, the clamps and guides are attached and the platen is reinstalled in the machine. This clearly involves a great expense which is limited to the particular machine. If the machine breaks or is down for service, the clamps and guides are not readily transferable to another machine. The use of many discrete guides and clamps on the platen face for supporting the mold base also compounds the problem of damage to the molding machine due to pieces of metal falling into the machine.
U.S. Pat. No. 4,714,421 issued to D'Agostino discloses a quick change system for mold bases having a T-shaped plate recessed in and attached to the back of each mold half. On the ejector side of the press, the entire ejector assembly is contained within a large clamp plate. The T-shaped plates are not readily interchangeable between mold bases. Also, the large clamp plate attached to the ejector side of the mold base limits the amount of available mold space in the injection molding machine.
The problem of changing mold bases is not limited to injection molding machines. Similar problems are presented in changing the die or mold in a stamping press. In both situations, the mold set weighs a substantial amount and must be handled carefully to avoid damage to the mold, die and press.
At the present time, there does not appear to be a simple system for interchanging mold bases in less than one hour. Also, there does not appear to be a simple system that would allow many different size mold bases to be equipped with a common ear plate which would enable the mold bases to be readily changed in a molding press.